Searching for Twitter users is an easy job once you know where to look, there are many directories which catalog Twitter users or directories where you can add yourself to help expand visibility.

Here are the top Twitter directories I use:
WeFollow – Grouping Twitter users and messages using #tags
Twellow – Directory of Twitter users by category
Social brand index – Directory of public companies
WhoShouldFollow – By adding your user name this API will find people you don’t follow which relate to your Twitter bio.
Just tweet it – Like WeFollow this directory adds you automatically, you just need to update your status.